The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has passed national acceptance and finished one pilot cycle of ‘Shared-Risk’ observations. It will start formal operation soon. In this context, this paper describes testing results of key fundamental parameters for FAST, aiming to provide basic support for observation and data reduction of FAST for scientific researchers. The 19-beam receiver covering 1.05–1.45 GHz was utilized for most of these observations. The fluctuation in electronic gain of the system is better than 1% over 3.5 hours, enabling enough stability for observations. Pointing accuracy, aperture efficiency and system temperature are three key parameters for FAST. The measured standard deviation of pointing accuracy is 7.9″, which satisfies the initial design of FAST. When zenith angle is less than 26.4°, the aperture efficiency and system temperature around 1.4 GHz are ∼0.63 and less than 24 K for central beam, respectively. The sensitivity and stability of the 19-beam backend are confirmed to satisfy expectation by spectral Hi observations toward NGC 672 and polarization observations toward 3C 286. The performance allows FAST to take sensitive observations for various scientific goals, from studies of pulsars to galaxy evolution.

Context. The spiral structure of our Milky Way Galaxy is not yet known. HII regions and giant molecular clouds are the most prominent spiral tracers. Models with 2−4 arms have been proposed to outline the structure of our Galaxy. Aims. Recently, new data of spiral tracers covering a larger region of the Galactic disk have been published. We wish to outline the spiral structure of the Milky way using all tracer data. Methods. We collected the spiral tracer data of our Milky Way from the literature, namely, HII regions and giant molecular clouds (GMCs). With weighting factors based on the excitation parameters of HII regions or the masses of GMCs, we fitted the distribution of these tracers with models of two, three, four spiral-arms or polynomial spiral arms. The distances of tracers, if not available from stellar or direct measurements, were estimated kinetically from the standard rotation curve of Brand & Blitz (1993, A&A, 275, 67) with R 0 = 8.5 kpc, and Θ 0 = 220 km s −1 or the newly fitted rotation curves with R 0 = 8.0 kpc and Θ 0 = 220 km s −1 or R 0 = 8.4 kpc and Θ 0 = 254 km s −1 . Results. We found that the two-arm logarithmic model cannot fit the data in many regions. The three-and the four-arm logarithmic models are able to connect most tracers. However, at least two observed tangential directions cannot be matched by the three-or four-arm model. We composed a polynomial spiral arm model, which can not only fit the tracer distribution but also match observed tangential directions. Using new rotation curves with R 0 = 8.0 kpc and Θ 0 = 220 km s −1 and R 0 = 8.4 kpc and Θ 0 = 254 km s −1 for the estimation of kinematic distances, we found that the distribution of HII regions and GMCs can fit the models well, although the results do not change significantly compared to the parameters with the standard R 0 and Θ 0 .